My favorite frame for a beach cruiser are the later Cleveland welding Roadmaster frames.
Long top tube and laid back seat mast make for a roomy comfortable ride. They are also very strong and readily available in the form of the reproduction Luxury Liner frame. There’s a couple on ebay now. You can search for a 50’s or 60’s built frame but will pay more.
I built the bike below using a reproduction Luxury Liner frame (USA made), forged Schwinn fork with front brake mount, Electra ape hanger bars and a bargain 7 speed wheel set. It is quite light since it runs alloy rims and is missing all the accessories.
I love the Schwinn straight bar and cantilever frames too and have one of each but being 6’2 I find them a little cramped compared to the Roadmasters.